Revivability of fermentative hydrogen producing bioreactors Bita Baghchehsaraee, George Nakhla*, Dimitre Karamanev, Argyrios Margaritis Department of Chemical and Biochemical Engineering, The University of Western Ontario, London, Ontario N6A 5B9, Canada article info Article history: Received 31 May 2010 Received in revised form 8 November 2010 Accepted 10 November 2010 Available online 13 December 2010 Keywords: Biological hydrogen production Dark fermentation PCR-DGGE CSTR Feed interruption Carbon mass balance abstract In this study we investigated the revivability of a continuous biological hydrogen producing reactor after a period of feed interruption. Before the feed interruption, the hydrogen production yield was 1.36 mol H 2 /mol glucose with butyric acid and acetic acid as the main metabolic products. However, after feed interruption, butyric acid formation completely stopped and the hydrogen yield decreased to 0.29 mol H 2 /mol glucose. Lactic acid, ethanol and acetic acid became the main metabolites after re-start up. Reduction of organic loading rate together with increasing the pH after the feed interruption resulted in an increase in the hydrogen yield to 0.7 mol H 2 /mol glucose. The microbial community dynamics showed complete elimination of Clostridium affiliated strains and predominance of Lactobacillus affiliated strains after the re-start up of the reactor. ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction Most of the world’s energy demand today is supplied by fast depleting fossil fuels. The atmospheric pollution by fossil fuels is not only unhealthy but might also cause significant climate changes globally [1]. Therefore, fossil fuels should be substituted with sustainable energy sources that do not contribute to pollution and green house effect. Hydrogen is considered to be the cleanest energy carrier because its combustion by-product is only water. It has also the highest energy yield (142 kJ/g) which is 2.75 times more than that of any hydrocarbon [2]. Among different biological methods for hydrogen production dark fermentation is regarded as one of the most promising alternatives for sustainable energy generation because of the high rate of hydrogen production and its potential of direct use of wastewater streams and organic wastes [3e5]. One of the characteristics of hydrogen production systems is their sensitivity to environmental conditions such as feed interruption which is mainly because of the fact that most of the hydrogen producers are restrict anaerobes. Therefore, any failure in the reactor operation may cause sporolation and wash out of the hydrogen producing community [5]. Working at low hydraulic retention times which is an inevitable feature of biological hydrogen production by mixed cultures critically compromises reactor performance and increases vulnerability to process upsets. The hydraulic retention time of the dark fermentative hydrogen production systems is usually main- tained between 3 and 12 h [6] to prevent the growth of slow growing methanogens in the reactor. Wash out of reactors biomass at low hydraulic retention times even without any operational failure has been reported in the literature [7,8]. Considering the large scale continuous hydrogen produc- tion, if an operational failure causes wash out in the system, re-inoculation and start up of the system will be accompanied by a huge cost and long term interruption in system operation. Reactor start up is an important and time-consuming phase for successful operation of continuous flow systems. * Corresponding author. Tel.: þ1 519 661 2111x85470; fax: þ1 519 850 2129. E-mail address: gnakhla@eng.uwo.ca (G. Nakhla). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 2086 e2092 0360-3199/$ e see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.11.038